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Extension tubes


New Member
can someone advise me as to the exposure compensation necessary with diferent extension tubes on an 80mm lens

thank you, not sure where to post this question....

A short table:

80 mm lens (infinity & close focus limit)+

no tube: 0 - 0.3 stops
8 mm tube: 0.2 - 0.5 stops
16 mm tube: 0.4 - 0.7 stops
8 mm + 16 mm tubes: 0.6 - 0.9 stops
32 mm tube: 0.8 - 1.0 stops
32 mm + 8 mm tubes: 1.0 - 1.2 stops
32 mm + 16 mm tubes: 1.2 - 1.4 stops
56 mm tube: 1.3 - 1.5 stops
The tables and explanation on the Clearsight site are good, but not quite it.

They ignore the effect of asymmetry in lens designs. However, the 80 mm lens is almost symmetrical, and the deviation is negligible.
The tabulated values for the longer lenses in particular do show a small but significant fault.